Acceptor compositions and method for oxygen enrichment processes

ABSTRACT

Special oxygen acceptor compositions for the production of oxygen in modified Brin-type processes. The compositions comprise a physical mixture of finely ground barium peroxide and dolomitic quicklime in which the weight percent of the dolomitic quicklime ranges up to about 92 percent. The use of dolomitic quicklime in conjunction with barium peroxide has been found to increase the oxygen production per mole of barium peroxide more than ten-fold. Typical operation conditions for production of oxygen in accord with the process utilizing the new material are 1-50 psia, at 1,350*-1,600*F during the reduction (oxygen production) half of the cycle, and 40-200 psia, at 1,300*-1,550*F during the oxidation half of the cycle. The cycle time for production is substantially decreased. The particle size of the barium peroxide in the composition mixture is preferably smaller than about 100 mesh, while the dolomitic quicklime is preferably smaller than about 40 mesh. The dolomitic quicklime must be prepared under conditions to insure that the final carbonate content of the dolomitic quicklime-barium peroxide mixture is such that the mole ratio of carbon dioxide to barium peroxide is less than 1.0. The composition may be in various forms: powder, granular, pelletized, coated on saddle supports and the like. In addition to increased oxygen production per mole of barium peroxide and reduction in cycle times, a significant reduction in the amount of barium oxides required to produce oxygen at any given rate is exhibited by the compositions.

States Patent 1 Huebler et al.

[ Nov. 20, 1973 ACCEPTOR COMPOSITIONS AND METHOD FOR OXYGEN ENRICHMENT PROCESSES [75] Inventors: Jack Huebler, Deerfield; Lester G.

Massey, Moreland Hills; Paul B. Tarman, Elmhurst, all of Ill.

[73] Assignee: Consolidated Natural Gas Service Co., Inc., Cleveland, Ohio 22 Filed: Apr. 7, 1972 211 Appl. No.: 242,153

[52] U.S. Cl 252/186, 23/281, 60/39.02, 423/579 [51] Int. Cl C01b 13/08 [58] Field of Search 252/186; 23/281; 423/579, 635; 60/39.02

[56] References Cited UNITED STATES PATENTS 2,486,530 11/1949 Jenness 252/186 3,324,654 6/1967 Squires 60/39.02 3,579,292 5/1971 Mullhaupt et al. 252/186 Primary Examinerl-lerbert B. Guynn Assistant Examiner-Irwin Gluck Attorney-Milinare, Allegretti, Newitt & Witcofi [57] ABSTRACT Special oxygen acceptor compositions for the production of oxygen in modified Brin-type processes. The compositions comprise a physical mixture of finely ground barium peroxide and dolomitic quicklime in which the weight percent of the dolomitic quicklime ranges up to about 92 percent. The use of dolomitic quicklime in conjunction with barium peroxide has been found to increase the oxygen production per mole of barium peroxide more than ten-fold. Typical operation conditions for production of oxygen in accord with the process utilizing the new material are 1-50 psia, at 1,350-l ,600F during the reduction (oxygen production) half of the cycle, and 40200 psia, at l,3001,550F during the oxidation half of the cycle. The cycle time for production is substantially decreased. The particle size of the barium peroxide in the composition mixture is preferably smaller than about 100 mesh, while the dolomitic quicklime is preferably smaller than about 40 mesh. The dolomitic quicklime must be prepared under conditions to insure that the final carbonate content of the dolomitic quicklime-barium peroxide mixture is such that the mole ratio of carbon dioxide to barium peroxide is less than 1.0. The composition may be in various forms: powder, granular, pelletized, coated on saddle supports and the like. In addition to increased oxygen production per mole of barium peroxide and reduction in cycle times, a significant reduction in the amount of barium oxides required to produce oxygen at any given rate is exhibited by the compositions.

20 Claims, 3 Drawing Figures Pmmmnmo I975 3.773.680

sum 10F 2 COM POSITION DIAGRAM MOLE FRACTION a Q INACTIVE MIXTURES LIZJ o g PREFERRED 40 E 0x 0 520 C 4 ACTIVE MIXTI'URES 0 O 0.2 0.4 0.6 0.8 1.0 2 L4 MOLE CO /MOLE B 0 PATENTEUHUVZO I975 SHEET 2 BF 2 QL/BAR UM PEROXIDE WT PATIO 00 o O 0 0 0 O 6 CARBON DlOXIDE/BARIUM PEROXIDE RATIO MOL/MOL EFFECT OF CARBON DIOXIDE ON MAXIMUM CONVERSION OF BARIUM PEROXIDE IN BARIUM PEROXlDE-DQL MIXTURE ACCEPTOR COMPOSITIONS AND METHOD FOR OXYGEN ENRICHMENT PROCESSES FIELD OF THE INVENTION This invention relates to acceptor compositions for use in producing oxygen and enriching air, by so-called oxygen absorbing processes, such as modified Brintype processes. More specifically, the invention relates to compositions of dolomitic quicklime with barium peroxide which greatly enhances the activity of barium peroxide in such processes and provides faster reaction rates and better gas conversions. This invention also relates to processes employing the new material.

BACKGROUND OF THE INVENTION Processes for the production of oxygen, which include the enrichment of air by increasing its total oxygen content above the approximately 21 percent found in air, can be broadly divided into two classes: 1) mechanical, and 2) chemical. The mechanical processes generally include compression of air followed by cryogenic distillation. Such processes from the point of view of energy and economics have resulted in their almost exclusive use.

Chemical processes include oxygen production as a result of electrolysis of water, and so-called absorption processes such as those of Brin and DuMotay. These latter processes involve the reversible absorption-desorption" of oxygen by chemical compounds under controlled conditions of temperature and pressure.

The DuMotay process of 1866 involves the use of sodium manganate which may be in liquid form. This process remains essentially a laboratory curiosity, and is not a significant commercial process.

The Brin-type processes are based on the 1851 discovery by Boussingault that barium oxide, when heated a dull red, absorbs oxygen, and when heated to higher temperature gave off the absorbed oxygen. This led to the first commercial production of oxygen starting in about 1881 and continuing for about 20 years by the Brin brothers of France. As described in the Brin British patent of 1885, No. 157, they used a three-step process which involved first, the removal of CO from air, then passing the dried Co -free air through or over a retort of baryta (barium oxide, BaO) at a temperature of 500 600C (932F 1,1 12F) to "absorb" oxygen, and third, the oxygen was withdrawn from the barium oxide by a vacuum creating means. The temperature ordinarily was raised to about 800C 1,472F) during the third stage. This gave rise to what is commonly known as the heat cycle variation of the Brin process. A complete cycle took from 3 to 4 hours.

In the Brin British patent of 1885, No. 151, the manufacture of the barium oxide used in the process of the No. 157 patent was described. A nitrate of baryta was heated to high temperature of from 1,000 -l,500C in a closed vessel and was then cooled in a vacuum to produce the baryta.

The Jensen British patent of 1880, No. 1416, was another Brin process patent in which compressed air was used in the retorts. This gave rise to the pressure cycle variation of the Brin process. The use of air under pressure apparently ensured a complete and uniform absorption" of oxygen in the entire mass of the barium oxide. In this process, the temperature was maintained relatively constant for economic reasons. Although authorities differ as to the exact pressure used, it has been variously reported that the air was forced in at a pressure of from 10 to 15 pounds or 25 to 30 psia, while the oxygen was drawn off under a vacuum of 13 to 14 pounds or 1 psia. While the cycle time was relatively short, being reported to be on the order of about 10 minutes, the output was low.

More recently, Squires US. Pat. No. 3,324,654 shows a Brin-type process for the simultaneous production of oxygen and power wherein the compressed air is let down through an expansion turbine to recover energy values in the compressed air. The oxygen absorbing bed is a solid composed of an intimate intermingling of tiny crystallites of barium oxide and magnesium oxide. In the process, the bed must be mixed periodically. The crystallites are prepared from a coprecipitated barium carbonate and magnesium carbonate mixture which is pelletized with active carbon and, optionally, a starch paste binder. These pellets are dried and heated to 1,200F under a CO atmosphere to decompose the MgCO to form MgO, and then further heated to 1,750F to 1,800F under N, to react" the carbon with the BaCO In a recent publication of Moriarty, Moriarty, John L., Jr., The Effects of Catalytic or Promotor Oxides on The Brin Process, Proc. Iowa Acad. Sci. 77, 360-78, April 10, 1971, the influence of 18 oxides as reaction promotors was studied and the results of 40 admixture experiments (apparently binary mixtures) were evaluated. The experimental evidence reported there by Moriarty led him to state that it supports the conclusion that the reversible BaO-BaO reaction is not, in general, substantially improved by the employment of foreign oxide additions. BaO was mixed, in several types of preparations, with the following oxides: La O MgO, Fe O C00, CuO, CdO, SiO CeO A1 0 ZnO, NiO, CaO, SrO, Ag O, MnO PbO, I-IgO, and Na O,. Moriarty reported that La O and MgO increase the oxygen yield rate when mixed with BaO, but that the physical arrangement of reaction bed and rapid evacuation procedures appeared critical.

In spite of the many variations in the Brin processes which have been tried in the last century, there today is no substantial commercial process for production of oxygen or enrichment of air involving the use of barium oxides. Many industrial processes employ oxygen or oxygen enriched air, for example, steel making, glass making, aerobic fermentation processes, sewage treatment and various combustion processes. There is thus a significant need for a reliable and economical chemical process for oxygen production or enrichment of air with oxygen.

OBJECTS It is among the objects of this invention to provide an improved Brin-type process for the production of oxygen and enrichment of air with oxygen.

It is another object of this invention to provide an improved oxygen enrichment process of the chemical type employing barium oxides.

It is another object of this invention to provide improved oxygen acceptor compositions for use in a chemical oxygen enrichment process.

It is another object to provide improved oxygen acceptor compositions and a process for their use which is reliable and economical.

It is another object of this invention to provide improved oxygen acceptor compositions and method for their use which exhibit faster reaction rates, better gas conversion, increased oxygen production and shorter cycle times than heretofore possible.

It is another object of this invention to provide an oxygen acceptor composition which has a relatively infinite lifetime in terms of cyclic reuse, and yet which is relatively simple to make, inexpensive, and can be stored and shipped under adverse conditions.

It is another object of this invention to provide an oxygen acceptor mixture comprising barium peroxide with dolomitic quicklime, which compositions show improved and unexpected results as compared to previously known compositions, and yet which are relatively insensitive to degradation by water vapor and inactivation by exposure to ambient atmospheric CO under normal storage conditions, as compared to BaO.

It is another object of this invention to provide a chemical process of the modified Brin-type which is commercially feasible as compared to laboratory curiosities of the prior art.

It is another object of this invention to enhance the inherent low activity of barium oxides and thus make Brin-type processes into commercial realities.

Still other objects of this invention will become evident from reading the following description.

SUMMARY OF THE INVENTION One aspect of this invention is the discovery that the addition of dolomitic quicltlime, hereinafter DQL, greatly enhances the activity of barium oxides in Brintype processes. A second aspect of this invention is the use of the bed material initially in the form of barium peroxide, BaO rather than a prior art use of barium oxide.

DQL itself is inactive yet promotes the activity of the barium oxides. Faster reaction rate and better gas conversions are obtained by the use of BaO -DQL compositions of this invention. The addition of DQL has been found to increase the overall oxygen production per mole of barium peroxide more than l-fold, and instantaneous rates as much as 23-fold.

Typical operating conditions for production of oxygen for enriching air in accord with the process aspect of this invention are: l-50 psia at l,350 1,600F during the reduction (oxygen production) half of the cycle and 40-200 psia at l,300 1,5 50F during the oxidation half of the cycle.

We have found that physical mixing of finely ground barium peroxide with DQL increases the activity of barium oxides in both the oxidation and reduction halves of the cycle. The weight percent DQL useful in the mixtures of our invention range from 1 92 percent. The particle size of the barium peroxide is preferably smaller than about 100 mesh. The DQL particle size is smaller than about 40 mesh, preferably smaller than about 80 to 100 mesh.

A critical aspect of this invention is the discovery that the oxygen acceptor composition must be relatively CO free. The BaO and DQL must be prepared and mixed under conditions which insure that the final carbonate content of the DQL-Ba0 mixtures of this invention are such that the mole ratio of carbon dioxide to barium peroxide is less than 1.0. We have also discovered that the DQL may be derived from a variety of naturally available dolomites, but which must be calcined under conditions which insure the final carbonate content of the mixture is less than 1.0 mol CO /mol B302.

In connection with this critical CO content, we have found that our material also provides the advantage that commercially available materials which are relatively CO free can be used. No expensive, and difficult to control chemical precipitation or decomposition steps are required in the preparation of our bed mixture of DQL-B210 We employ only simple blending, and optionally, compaction of the two raw materials required.

Another important aspect of the invention is the use of barium peroxide instead of barium oxide in the mixture with the DQL. The use of barium peroxide significantly improves oxygen activity and minimizes the probability of hydration (formation of barium hydroxide through absorption of water), and carbonation (formation of barium carbonate), during preparation and storage of the active bed mixture. We have found that one source of inactivity and reduction lifetime of bed materials is due to hydration and carbonation. Thus, we provide the initial bed material in an oxidized state, and our process involves termination of the process, for reasons of shutdown for repairs and the like, in the oxidation stage to insure the barium is in the peroxide state.

While we do not wish to be bound by theory, it is believed that starting initially with BaO rather than the prior art use of BaO, provides naturally pre-formed and pre-filled oxygen sites in the composition matrix. The initial evolution of oxygen produces a porosity in the matrix, and the oxidation half of the cycle starts with openings of the appropriate molecular size in the matrix structure. As noted above, the prior art loosely uses the term absorption in connection with barium bed materials. However, since chemical reaction occurs in reversibly transforming solid BaO to BaO the term absorption is a misnomer. While we do not wish to be bound by terminology, we believe that the term acceptor more generically describes what happens to the mixtures of this invention during operation, whether the reversible, temporary binding of the oxygen be physical adsorption, of chemical bonding of various types. The use of our acceptor mixtures thus includes use in the prior art processes as they called for absorbent bed materials. We are sure that oxidation and reduction of the barium oxide-peroxide couple does occur in our mixtures, but it is also possible that physical adsorption occurs, since our bed material is a complex, synergistic mixture of the barium oxides with DQL.

In the process of this invention using our new DQL-BaO- mixtures, we may employ variation in pressure and/or temperature in the two halves of the cycle. In addition to enhancement of activity, we have discovered that the DQL provides still another advantage. That is, the high specific heat of the DQL relative to that of the barium oxides serves to store heat during the exothermic oxidation, and permits release of heat during the endothermic reduction. In operation, because the BaO and DQL are in intimate mixture, endothermic and exothermic heats are provided for in close proximity to active sites; heat transport over more than infinitesimal distances is not required. This results in a reduction of overall temperature fluctuations which are detrimental to cyclic operation and gas conversions.

We are thus able to employ reactors in which no heat exchange equipment is required for removal or addition of reaction heat. Likewise, our process does not require raking or rabbling the bed material from near the inlet entrance to the interior to compensate for non-uniform reaction or heat distribution.

The compositions of this invention may be used with any of the Brin-type processes, whether they be of the basic Erin-type, the thermal or pressure cycle type processes, or of the more recent energy recovery modification as set forth in Squires US. Pat. No. 3,324,654. Our preferred mode of operation with the compositions of this invention is to produce oxygen, or oxygen enriched air, by cyclicly varying pressure at relatively constant temperature, so that the barium oxide in the bed is oxidized to barium peroxide using relatively high pressure air, and the barium peroxide is reduced to barium oxide using lower pressure air. The oxygen generated in the reduction may be recovered relatively pure, or may be mixed with purging lower pressure air, thereby consistently enriching its oxygen content to as much as 40 percent. The oxygen or enriched air may be used in all combustion processes, in the production or iron, steel, and glass, and in chemical processing such as synthesis gas production, sewage treatment, stream aeration, oxygen pyrolysis of municipal solid waste to produce fuel gas, and the like.

The DQL-BaO mixtures of this invention may be used in various forms, either loose or compacted, the latter in such forms as pellets or on saddle supports.

The invention is described in more detail below with reference to the following figures of which:

FIG. I is a trilinear diagram of the three components of the acceptor mixtures in accordance with this invention as defined by the area between the lines A and B;

FIG. 2 illustrates the critical nature of the mole ratio of CO /BaO as a function of the weight percent DQL in the bed material mixtures of this invention, and which additionally shows the preferred mixtures of this invention; and

FIG. 3 illustrates the effect of the maximum cyclic conversion as a function of the mole ratio of CO /BaO mixture for a typical range of mixtures of varying the weight ratios of DQL/BaO In the following detailed description, the examples given therein are by way of illustration and not by way of limitation.

DETAILED DESCRIPTION AND EXAMPLES Mixtures in accordance with our invention may be prepared from various sources of dolomitic quicklime and barium peroxide. It is critical, however, to the activity of the mixtures in accordance with our invention that the carbon dioxide/barium peroxide mole ratio in the mixture be below 1.0, since we have found that the cyclic conversion drops to 0 as the carbon dioxide/- barium peroxide mole ratio approaches 1.0. Conversely, we have found that as the carbon dioxide content in the DQL is reduced below this critical mole ratio value of 1.0 CO /BaO the mixture shows a corresponding increase in the maximum cyclic conversion. Further, as the weight ratio of DQL in the DQL-Ba0 mixtures increases, the critical value of the CO /BaO mol ratio decreases in a non-linear fashion.

Typically, the dolomitic quicklime may be obtained from commercial sources (such as the Marblehead Lime Company or Pfizer Chemical Company) as derived from a natural, domestic dolomite. As received, the dolomite has a large particle size on the order of from 1 to 2 inches in diameter (1 inch X 0 to 2 inches X 0), and may contain more or less than the critical CO content. These large particles may then be processed by calcining in a gas-fired tunnel kiln at temperatures between l,900 2,000F for a period of four hours to form DQL. This product should be unslaked. The kiln product is then crushed to below one-fourth inch in a jaw crusher, and then to below about 40 mesh, preferably below 80 to 100 mesh in a hammer mill. Optionally, the DQL may be purchased commercially, and if necessary crushed to the appropriate mesh size. The DQL should be assayed for CO content after calcining and crushing, or upon receipt in the case of commercial DQL, to insure meeting the criteria for the final mixtures. The CO content can be controlled by adjusting the length and temperature of the calcining schedule. The dolomite is a natural mineral composed of calcium and magnesium carbonates. The corresponding natural dolomitic quicklimes typically range from 3:1 to 1:3 MgO/CaO on a mole to mole basis. While we prefer to use a natural compound containing MgO and CaO, prepared mixtures or compounds of MgO and CaO may be substituted in place of the dolomitic quicklime in accordance with this invention.

The BaO is also commercially available (e.g., Barium & Chemicals, Inc., or Baker Chemical Co.), and is preferably below about 100 mesh. Technical or reagent grade Ba0 is satisfactory, but more crude forms may be obtained and purified by known processes. BaO may be employed, but must be converted to BaO: to maintain the activity, integrity, and stability of the mixture with DQL. The BaO, should be routinely assayed to determine that its CO content is low enough to assure negligible loss in activity. Where the CO content is high, the BaO may be heated to from about 850950C to drive off the C0,. If the BaO is melted or becomes sintered, it must be reground to the desired mesh. Ba0 also is available as a hydrated BaO '8I-I O, which evolves the hydrated water at 100C. Anhydrous Ba0 is preferred, and as referred to herein, BaO means anhydrous BaO While various forms of the mixture may be used, e.g., loose powder in fluidized bed, pellets, or a supported mixture, we prefer to use a pellet form. However, discoveries in connection with pellet forms of our mixture are not part of this generic invention, and are disclosed and claimed in a co-pending application filed or even date herewith, Ser. No. 241,957, the disclosure of which is incorporated herein by reference.

EXAMPLES 1 5 A series of five mixtures having DQL BaO weight ratios of 9.0, 4.0, 2.3, 0.67, and 0 were prepared, in which the BaO is -l00 mesh and DQL is -200 +325 mesh. These weight ratios correspond respectively to 90/10, 80/20, /30, 40/60, and 0/100 weight percent ratio mixtures. In a series of test runs, psig air was used for oxidation, and 2 psig air was used for reduction at a temperature of 1,450F, :15F, and the effect of carbon dioxide content on activity and maximum cyclic conversion of the DQL-BaO mixture was ascertained by weight change measurements made in a thermobalance. In order to obtain controlled amounts of carbon dioxide in the mixtures, a special sample of incompletely calcined DQL was assayed for the carbon dioxide content. This DQL was then added in measured amounts to a completely calcined DQL sample, which had been assayed and found to have essentially no carbon dioxide therein, to provide a series of samples having a final CO lBaO mole ratios in the range of from O to 1.0.

These tests, and others discussed below, were run in a standard thermobalance (thermogravimetric balance) of the following general construction. The sample contained in a porous (wire screen) basket is suspended in a heated reaction zone by a wire attached to a weight sensitive transducer located in the upper, colder portions of the reactor. Gas of the desired composition is passed over the suspended sample, reacting it and changing its weight. The transducer transmits these weight changes to a recorder producing a continuous weight record which can be used to determine the particular reaction rate being studied. With the thermobalance, it is possible to continuously monitor the weight change due to reaction of a solids sample and by simple calculation determine the conversion percent and/or rate.

From the run data the relationship between the maximum cyclic conversion of BaO in percent and the CO,/Ba mole ratio was determined. This relationship, for representative weight percent values of DQL and mole ratios of co /B00 is set forth in tabular form in Table 1.

mole ratio of CO /BaO must be decreased to render the mixture active, and must be decreased in a nonlinear fashion in accordance with the curves shown.

Within the region of active mixtures to the left and below curve C in FIG. 2, we prefer the mixtures shown in the area lined between curve D and the horizontal line which intercepts the DQL ordinant at about percent. These mixtures show superior activity in terms of conversion, reduced cycle time and oxygen production, and are therefore preferred mixtures. Curves C and D can be mathematically approximated from the empirical data as follows:

Curve C:

Wt. percent DQL [1,500 (l Z)]/(l6 lSZ); O

s Z s 1 Equation 1; Curve D:

Wt. percent DQL (1,272 l,500Z)/(l3.72

152); 0 Z s 0.82 Equation 2;

where Z mole Co /mole BaO This will permit one to determine the maximum amount of DQL permissible in a final mixture to prevent it from being inactive, or to be one of the preferred mixtures. The above equations may be rearranged to determine the maximum permissible CO in a mixture ofa given weight percent DQL.

EXAMPLE 6 A second series of tests were run using the thermo- DQL-BA RIUM PE ROXIDE MIXTURES Weight Mam'mum cyclic conversion, percent for each of the following percent mole ratios 002/8802 Example DQL in number mixture 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.7 0.3 0.0 1.0

A zero cyclic conversion value indicates no activity.

These values may be plotted graphically, the maximum balance as above described. In this series, various cyclic conversion of BaO in percent as a function of weight ratios of dolomitic quicklime to barium oxide the C0,/Ba0 ratio in mol/mol to produce a series of ranging from 0/100 through 100/0 were used. Also varnegative slope straight lines, as shown on FIG. 3. The ious types of dolomitic quicklimes were used in order X-axis intercept for each mixture is the critical CO to vary the percentage ratio of MgO to CaO. Activities content ratio which should not be exceeded. This value of the resultant dolomitic quicklime-barium peroxide is 0.95 for a 40/60 mix, 0.84 for a 70/30 mix, 0.73 for mixtures were determined. The oxidation pressure was an 80/20 mix, and 0.39 for a 90/10 mix. Critical values as above, 80 psig air, and reduction pressure was 2 psig for other mixtures may be determined by graphical inair. The barium peroxide used was -l00 mesh, the terpolation or simple testing following the above de- DQL was 200 +325 mesh, and the temperature of 0pscribed procedures. These examples also illustrate the eration was 1,450F il5F. inverse relationship between CO /BaO mole ratio and The results of these series of tests are shown in a tricyclic conversion. linear graph in FIG. 1. Each apex of the graph repre- FIG. 2 illustrates both active and preferred mixtures sents the pure compound as indicated. The rulings parin accordance with this invention in terms of the weight allel to a side of the triangle measure the mole fraction percent DQL in the mixture as a function of the mole of compound identified at the opposite apex. A binary Co /mole B210 ratio, with the weight percent DQL mixture is represented by a point on a sie of the trianlying between 0 to 100 percent, and the mole ratio of gle. In particular, all dolomitic quicklime compositions 00 /1300, in the mixture ranging from 0 to 1.0. We have values lying on the horizontal base of the triangle. have discovered that inactive materials lie to the right In terms of preferred activity, those compounds having and above the best-fit" curve C, whereas the mixtures compositions falling between the upper curved line A of DQL BaO lying below and to the left of best fit" and the lower curved line B on the graph are comcurve C are active mixtures which may be used in Brinpounds falling within the scope of this invention. Each type processes in accordance with this invention.

Surprisingly, as the weight percent DQL increases in the mixtures in accordance with this invention, the

point on the graph represents one of the runs of this Example, as indicated by the numbers 1 21 associated with the data points on the graph.

The upper curve A intercepts the MgO-BaO; binary (left side of triangle) at 0.57, i.e., 57% BaO intercepts the equimolar MgO-CaO line (vertical height) at 0.69, i.e., 69% Ba and intercepts the CaO-BaO binary (right side of triangle) at 0.75, i.e., 75% BaO The lower curve B intercepts the MgO-BaO binary at 0.05, i.e. 5% BaO intercepts the equimolar MgO-CaO line at 0.02, i.e., 2% Bao and intercepts the CaO-BaO binary at 0.07, i.e., 7% BaO There is no intercept of either curve along the MgO-CaO binary.

EXAMPLE 7 Another series of runs was made under the conditions described above to determine the effect of particle size and concentration of DQL on the activity of barium peroxide. The barium peroxide used in the mixture was 100 mesh, and the oxidation pressure, reduction pressure, and temperatures were as above stated. In this series of tests, the percentage cyclic conversion and weight ratio of DQL of barium peroxide was predetermined. The particle size of the DQL was varied to determine the effectiveness of the mixture in terms of the cycle time in minutes, and oxygen production in standard cubic feet per hour-pound of barium peroxide. The cycle time and oxygen were determined from thermobalance data.

TABLE 2.EFFECT OF PARTICLE SIZE AND CONCEN- TRATION OF CALCINED DOLOMITE (DQL) ON ACTIVITY OF BARIUM PEROXIDE Test conditions Test results Cyclic Weight conver- Variable stud- Oxygen ratio sion, ied, particle Cycle production, Test run DQL- percent size of DQL, time, 5.0.1. r.- number BaOz chosen U.S.S. sieve nnn. 1b. BaOz 0/100 10. 6 N.A. 9. 2 0. 77 /80 21. 2 200+325 7. 8 1. 81 60/40 15. 9 200+325 2. 8 3. 80 80/20 21. 2 -200+325 1. 6 8. 87 100/0 0 200+325 N.A. 0 80/20 21. 2 80+200 3. 3 4. 35 80/20 21. 2 40+80 3. 2 4. 44

Run No. l is a comparison run showing the activity of barium oxide-barium peroxide. No DQL was used. For a cyclic conversion of 10.6 percent, a cycle time of 9.2 minutes results, which corresponds closely to the best values reported for the basic Brin process. The oxygen production is also a low 0.77 standard cubic foot per hour-pound barium peroxide. This confirms the present-day commercial impracticality of the basic Brin process.

Test runs 2 4 illustrate that as the weight of dolomitic quicklime in the mixture is increased from 20 percent to 80 percent, at a constant size range of between -200 to +325 mesh, the cycle time drops and oxygen production increases dramatically, even when the percent cyclic conversion is prechosen to be from 50 to 100 percent higher than with pure barium oxideperoxide (run l). The presently preferred particle size range of the DQL ranges from 200 to +325 mesh, but may be on the order of 40 mesh or larger. For the 80/20 mix of our invention, the oxygen production in standard cubic feet per hour-pound BaO, is more than i 1.5 times that for straight barium peroxide (compare runs 1 and 4). The cycle time also drops from 9.2 minutes to 1.6 minutes, a 600 percent improvement in cycle time (a drop from 552 seconds to 96 seconds).

Test run 5 is also a comparative example showing that pure DQL showed no activity by itself. From the comparison of runs 1 and 5 with run 4, we believe the DQL properly may be termed a promoter. Since the mixture shows such startling and improved results, it also properly may be termed synergistic. A mathemetical treatment of typical run data shows that some of the B210, is apparently bound by the DQL in a ratio of about 3 moles BaO per 100 moles of DQL, and may in part be responsible for the observed increase in activity.

Runs 4, 6 and 7 compare the effect of particle size on the activity of the mixture. In all three runs, the weight ratio of DQL/BaO was fixed at a ratio of /20 (4:1) and the cyclic conversion percentages were held constant. The particle size of the DQL was increased from the range of 200 +325 to --40 +80. It is significant that as the DQL particle size was increased, the cycle time doubled and the oxygen production dropped to one-half of test run 4. A comparison of runs 6 and 7 shows that although above the particle size range of 80 +200 mesh for a given cyclic conversion the cycle time and oxygen production is relatively constant, a 40 mesh size DQL still yields a commercially suitable oxygen production rate. Operation of a Typical Process Using the Acceptor Mixtures of This Invention In operation, The DQL-Ba0 oxygen acceptor composition of our invention is charged into a suitable reactor and gradually heated up to the operating temperature range of from l,350- 1,600F for commencing the operation at the reduction (oxygen production) half of the cycle. Air is pumped through the reactor at a pressure in a range of from l-50 psia at which time the BaO of the initial mixture is converted by reduction to BaO A 0 The air is let in for from about 0.8 to 4.0 minutes; the BaO is stripped of (releases) its combined oxygen to the purging air. The purging air leaves the reactor enriched to as much as 40 percent total oxygen concentration, and may be used as such directly in the various industrial processes described above. In the alternative, rather than purging the bed with air, the inlet side of the reactor may be valved closed, and a vacuum drawn to producesubstantially pure oxygen.

The reactor is then switched to the oxidation half of the cycle with air passing either co-currently or counter-currently, relative to the direction of flow during the reduction, through the bed at a pressure of from 40 200 psia at the bed temperature of from-1,300"- l,550F. During the oxidation half, the barium oxide then in the bed mixture combines with one-half O to produce barium peroxide. The time range for this half of the cycle is substantially the same as for the reduction half of the cycle. The air-depleted in oxygen may be ejected as waste gas to the atmosphere, or may be used in further processes to recover the nitrogen gases or energy therefrom.

As with other Brin-type processes, both the water vapor and carbon dioxide should be removed from the air let into the reactor, for example, by passing the air through various guard chambers containing conventional CO, and water absorbents.

The improved composition mixtures of our invention may be used in fluidized or static beds. We presently prefer to use them in a static bed, and such a bed does not require periodic raking, rabbling, or turning" to move that bed material which is closest to the inlet into the interior of the bed. For fluidized bed operation we prefer to first mix the BaO with DQL, compress the mixture into briquettes, and crush the briquettes to the desired powder size. The preferred powder is thus a powder of BaO -DQL, rather than particles of BaO mixed with particles of DQL. This assists in inhibiting the tendency of Ba to plate out of the mixture on reactor surfaces during fluidized operation.

The improved compositions can be used in accordance with the above operation with either the temperature or the pressure variations of the Brin process, or with various combinations of both temperature and pressure.

It should be understood that the terms mixture and composition are used herein in a broad, generic sense, and are not meant to connote a particular final form of the acceptor material as used in a process. Thus the terms encompass the defined acceptor materials of this invention whether they be loose mixtures, frits, pellets, crystal mixtures, solid solutions in whole or in part, coatings of Ba0 on DQL, or coatings of any phase or form on an inert support, regardless of the final shape or form. Likewise, the term stripping" refers broadly and generically to the mechanism of oxygen removal from the Ba0 during the reduction half of the cycle, whether the function be physical desorption (reverse of adsorption) or involve chemical bond breaking, and includes the prior art loose use of the term desorption. Preparation of DQL-BaO Mixtures An important advantage of the mixture of our invention which should not be minimized is the fact that the mixture is easy to prepare from readily available commercial materials. The DQL-BaO mixture can be shipped with minimal precautions and stored over long periods of time without loss of activity. The mixture does not require preactivation and can be used directly in reactors without long, expensive and complicated calcination or reactivation procedures.

Heretofore, barium oxide has been used and has presented extremely complex problems in the preparation, shipment and storage. Barium oxide is highly hygroscopic, forming barium hydroxide with water vapor from the air. Compositions employing barium oxide pick up so much water that they become moist and lost their integrity. Reactors packed with such material tend to cake and become impervious to the flow of gas therethrough. Likewise, such material can become so caked during shipment or storage as to be relatively useless.

Further, barium oxide used alone or with other materials is susceptible to carbonation (the formation of barium carbonate) during preparation, transport and storage. The barium carbonate is substantially inactive in Brin-type processes. We have discovered that carbonation of barium oxide over a period of time is a major factor in inactivation of beds, and in shortening th shelf life of stored barium oxide-containing materials. In contrast, our DQL-BaO- mixture exhibits long lifetimes without the disadvantages of both hydration and carbonation. Likewise, during extensive continuous cyclic operation the material of our invention retains its full activity without loss of integrity. We have not yet observed any limitations on either shelf life or cycle lifetime, over a year of storage and 9 months of operation.

By way of example, powdered BaO and an /20 mixture of DQL and BaO powders were exposed to ambient atmosphere to observe weight gain due to hydration and/or carbonation. The BaO showed a percent weight gain in 23.5 hours, whereas the DQL/Ba0 gained only 1.4 percent in 1 16.5 hours. The weight gain was found to be ascribable to the DQL, since in 162 hours a sample of DQL gained 2.3 percent of its weight.

The powder, granules, pellets or supported forms of the mixtures or our invention may be prepared under commercial factory conditions, bagged, shipped and stored over long periods of time at the point of use without danger of inactivation. Of course, the material should not be abused, and it is prudent to afford it basic protection from harsh conditions of water and high CO atmospheres, such as by using conventional selfsealing drums, plastic lined, resin impregnated paper bags, or other sealed containers. When ready for use, the bags or drums of acceptor composition in accordance with this invention may be dumped directly into the reactors and put on stream as fast as they can be heated up. No special activation, chemicals or procedures are required.

A corollary of our discoveries in this regard is that in operation, when a reactor must be shut down for whatever reason, for example, for repairs or for stopping production through termination of need, the bed mixture should be oxidized to insure that the barium is in the peroxide state. The reactor can then be cooled and left as such for future use, or the mixture may be removed for transport or storage.

In contrast to the complex crystallites heretofore suggested by the prior art, no expensive chemical preparations or decomposition steps are required in the preparation of the compositions of our invention. Only simple blending and, optionally, compaction of the two raw materials is required. Likewise, extreme criticality in physical arrangement of reaction bed and rapid evacuation procedures do not appear the case with our composition.

ln operation, the DQL has a high specific heat relative to that of the barium oxides. This results in an important advantage of the composition in accordance with this invention; the DQL serves to store heat during the exothermic oxidation half of the cycle. This heat is then ready within the bed itself for release during endothermic reduction. This reduces the overall temperature fluctuations within the bed which is detrimental to cyclic operation and gas conversions. More importantly, this results in being able to omit the use of heat exchange equipment for removal or addition of the large heat or reaction.

As noted above, the use of the DQL improves the activity of the barium oxide in cyclic operation and allows operation at cycle times on the order of l-2 minutes as compared to 3-4 hours in the basic Brin process and 10 minutes for pure barium oxide. This in turn permits a significant reduction in the amount of barium oxide required to produce oxygen at any given rate.

It should be understood that within the spirit of this invention, one of ordinary skill in the art can make various modifications yet remain within the scope of this invention. We therefore wish the scope of the invention to be determined by the appended claims, interpreted in the light of this specification if need be, as broadly as the prior art will permit.

We claim:

1. An oxygen acceptor composition comprising a mixture of BaO MgO, and CaO in which the mole ratio of CO to BaO is less than 1.0, and mole percentages of CaO, BaO and MgO lie between the curves A and Bin FIG. 11.

2. An oxygen acceptor composition as in claim 1 wherein said mixture is a binary composition of BaO- with a compound of the oxides of Mg and Ca.

3. An oxygen acceptor composition as in claim 2 wherein said Mg and Ca oxides compound is derived from a naturally occurring dolomite.

4. An oxygen acceptor composition as in claim 3 wherein said derived compound is a dolomitic quicklime.

5. An oxygen acceptor composition as in claim 3 wherein the mole ratio of Mg/Ca ranges from 3:1 to

6. An oxygen acceptor composition as in claim 3 wherein said dolomite is calcined at high temperature to remove CO; to a level such that the CO /BaO mole ratio in said mixture is less than about 0.84.

7. An oxygen acceptor composition as in claim 2 wherein the weight percent of said Mg and Ca oxide compound in the mixture is less than about 92 percent.

8. An oxygen acceptor composition as in claim 4 wherein the weight percent of said dolomitic quicklime in the mixture is selected in accordance with the relationship:

Weight percent DQL 5 [1,500 (l Z)]/(l6 152,) where Z mole CO /mole Ba0 in the mixture, and 0 s 2 s l.

9. An oxygen acceptor composition as in claim 8 wherein said compositions is formed from dolomitic quicklime in discrete particles of size below about 40 U. S. mesh.

10. An oxygen acceptor composition as in claim 9 wherein said dolomitic quicklime particles are below about 80 U. S. mesh.

11. An oxygen acceptor composition as in claim 10 wherein said dolomitic quicklime particles are in the range of from 200 to +325 U. S. mesh.

12. An oxygen acceptor composition as in claim 8 wherein said composition is formed from BaO in discrete particles of size below about 100 U. S. mesh.

13. An oxygen acceptor composition as in claim 4 wherein the weight percent of said dolomitic quicklime in the mixture is an amount of a about 30 weight percent selected in accordance with the relationship:

Weight percent DQL s (1,272 l,500Z)/( 13.72

152), where Z mole Co /mole BaO- in the mixture, and 0 Z s 0.82.

14. An oxygen acceptor composition as in claim 13 wherein said composition is formed from dolomitic quicklime in discrete particles of size below about 40 U. S. mesh.

15. An oxygen acceptor composition as in claim 14 wherein said dolomitic quicklime particles are below about U. S. mesh.

16. An oxygen acceptor composition as in claim 15 wherein said dolomitic quicklime particles are in the range of from 200 to +325 U. S. mesh.

17. An oxygen acceptor composition as in claim 13 wherein said composition is formed from BaO in discrete particles of size below about U. S. mesh.

18. An oxygen acceptor composition as in claim 1 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules, c) pellets, and d) a coating on an inert support.

19. An oxygen acceptor composition as in claim 9 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules c) pellets, and d) a coating on an inert support.

20. An oxygen acceptor composition as in claim 14 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules, c) pellets,

and d) a coating on an inert support. 

2. An oxygen acceptor composition as in claim 1 wherein said mixture is a binary composition of BaO2 witH a compound of the oxides of Mg and Ca.
 3. An oxygen acceptor composition as in claim 2 wherein said Mg and Ca oxides compound is derived from a naturally occurring dolomite.
 4. An oxygen acceptor composition as in claim 3 wherein said derived compound is a dolomitic quicklime.
 5. An oxygen acceptor composition as in claim 3 wherein the mole ratio of Mg/Ca ranges from 3:1 to 1:3.
 6. An oxygen acceptor composition as in claim 3 wherein said dolomite is calcined at high temperature to remove CO2 to a level such that the CO2/BaO2 mole ratio in said mixture is less than about 0.84.
 7. An oxygen acceptor composition as in claim 2 wherein the weight percent of said Mg and Ca oxide compound in the mixture is less than about 92 percent.
 8. An oxygen acceptor composition as in claim 4 wherein the weight percent of said dolomitic quicklime in the mixture is selected in accordance with the relationship: Weight percent DQL < or = (1,500 (1 - Z))/(16 - 15Z,) where Z mole CO2/mole BaO2 in the mixture, and 0 < or = Z < or =
 1. 9. An oxygen acceptor composition as in claim 8 wherein said compositions is formed from dolomitic quicklime in discrete particles of size below about 40 U. S. mesh.
 10. An oxygen acceptor composition as in claim 9 wherein said dolomitic quicklime particles are below about 80 U. S. mesh.
 11. An oxygen acceptor composition as in claim 10 wherein said dolomitic quicklime particles are in the range of from -200 to +325 U. S. mesh.
 12. An oxygen acceptor composition as in claim 8 wherein said composition is formed from BaO2 in discrete particles of size below about 100 U. S. mesh.
 13. An oxygen acceptor composition as in claim 4 wherein the weight percent of said dolomitic quicklime in the mixture is an amount of > or = about 30 weight percent selected in accordance with the relationship: Weight percent DQL < or = (1,272 - 1,500Z)/(13.72 - 15Z), where Z mole CO2/mole BaO2 in the mixture, and 0 < or = Z < or = 0.82.
 14. An oxygen acceptor composition as in claim 13 wherein said composition is formed from dolomitic quicklime in discrete particles of size below about 40 U. S. mesh.
 15. An oxygen acceptor composition as in claim 14 wherein said dolomitic quicklime particles are below about 80 U. S. mesh.
 16. An oxygen acceptor composition as in claim 15 wherein said dolomitic quicklime particles are in the range of from -200 to +325 U. S. mesh.
 17. An oxygen acceptor composition as in claim 13 wherein said composition is formed from BaO2 in discrete particles of size below about 100 U. S. mesh.
 18. An oxygen acceptor composition as in claim 1 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules, c) pellets, and d) a coating on an inert support.
 19. An oxygen acceptor composition as in claim 9 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules c) pellets, and d) a coating on an inert support.
 20. An oxygen acceptor composition as in claim 14 wherein said mixture is in a form selected from: a) finely divided discrete particles, b) granules, c) pellets, and d) a coating on an inert support. 